When an error occurs during a call to any of the DEC C RTL functions, the function returns an unsuccessful status. Many RTL routines also set the external variable errno to a value that indicates the reason for the failure. You should always check the return value for an error situation.
The <errno.h> header file declares errno and symbolically defines the possible error codes. By including the <errno.h> header file in your program, you can check for specific error codes after a DEC C RTL function call.
At program startup, the value of errno is 0. The value of errno can be set to a nonzero value by many DEC C RTL functions. It is not reset to 0 by any DEC C RTL function, so it is only valid to use errno after a DEC C RTL function call has been made and a failure status returned. Table 4-2 lists the symbolic values that may be assigned to errno by the DEC C RTL.
| Symbolic Constant | Description |
|---|---|
| E2BIG | Argument list too long |
| EACCES | Permission denied |
| EADDRINUSE | Address already in use |
| EADDRNOTAVAIL | Can't assign requested address |
| EAFNOSUPPORT | Address family not supported |
| EAGAIN | No more processes |
| EALIGN | Alignment error |
| EALREADY | Operation already in progress |
| EBADF | Bad file number |
| EBADCAT | Bad message catalogue format |
| EBADMSG | Corrupted message detected |
| EBUSY | Mount device busy |
| ECANCELED | Operation canceled |
| ECHILD | No children |
| ECONNABORTED | Software caused connection abort |
| ECONNREFUSED | Connection refused |
| ECONNRESET | Connection reset by peer |
| EDEADLK | Resource deadlock avoided |
| EDESTADDRREQ | Destination address required |
| EDOM | Math argument |
| EDQUOT | Disk quota exceeded |
| EEXIST | File exists |
| EFAIL | Cannot start operation |
| EFAULT | Bad address |
| EFBIG | File too large |
| EFTYPE | Inappropriate operation for file type |
| EHOSTDOWN | Host is down |
| EHOSTUNREACH | No route to host |
| EIDRM | Identifier removed |
| EILSEQ | Illegal byte sequence |
| EINPROGRESS | Operation now in progress |
| EINPROG | Asynchronous operation in progress |
| EINTR | Interrupted system call |
| EINVAL | Invalid argument |
| EIO | I/O error |
| EISCONN | Socket is already connected |
| EISDIR | Is a directory |
| ELOOP | Too many levels of symbolic links |
| EMFILE | Too many open files |
| EMLINK | Too many links |
| EMSGSIZE | Message too long |
| ENAMETOOLONG | File name too long |
| ENETDOWN | Network is down |
| ENETRESET | Network dropped connection on reset |
| ENETUNREACH | Network is unreachable |
| ENFILE | File table overflow |
| ENOBUFS | No buffer space available |
| ENODEV | No such device |
| ENOENT | No such file or directory |
| ENOEXEC | Exec format error |
| ENOLCK | No locks available |
| ENOMEM | Not enough core |
| ENOMSG | No message of desired type |
| ENOPROTOOPT | Protocol not available |
| ENOSPC | No space left on device |
| ENOSYS | Function not implemented |
| ENOTBLK | Block device required |
| ENOTCONN | Socket is not connected |
| ENOTDIR | Not a directory |
| ENOTEMPTY | Directory not empty |
| ENOTSOCK | Socket operation on non-socket |
| ENOTSUP | Function not implemented |
| ENOTTY | Not a typewriter |
| ENWAIT | No waiting processes |
| ENXIO | No such device or address |
| EOPNOTSUPP | Operation not supported on socket |
| EPERM | Not owner |
| EPFNOSUPPORT | Protocol family not supported |
| EPIPE | Broken pipe |
| EPROCLIM | Too many processes |
| EPROTONOSUPPORT | Protocol not supported |
| EPROTOTYPE | Protocol wrong type for socket |
| ERANGE | Result too large |
| EREMOTE | Too many levels of remote in path |
| EROFS | Read-only file system |
| ESHUTDOWN | Can't send after socket shutdown |
| ESOCKTNOSUPPORT | Socket type not supported |
| ESPIPE | Illegal seek |
| ESRCH | No such process |
| ESTALE | Stale NFS file handle |
| ETIMEDOUT | Connection timed out |
| ETOOMANYREFS | Too many references: can't splice |
| ETXTBSY | Text file busy |
| EUSERS | Too many users |
| EVMSERR | OpenVMS-specific non-translatable error code |
| EWOULDBLOCK | I/O operation would block channel |
| EXDEV | Cross-device link |
You can translate the error codes to a message, similar to that found in UNIX systems, by using the perror or strerror function. If errno is set to EVMSERR, perror cannot translate the error code, and prints the following message, followed by the OpenVMS error message associated with the value:
%s:nontranslatable vms error code: xxxxxx vms message:
In the message, %s is the string you supply to perror; xxxxxx is the OpenVMS condition value.
If errno is set to EVMSERR, then the OpenVMS condition value is available in the vaxc$errno variable declared in the <errno.h> header file. The vaxc$errno variable is guaranteed to have a valid value only if errno is set to EVMSERR; if errno is set to a value other than EVMSERR, the value of vaxc$errno is undefined.
See also the strerror function in the Reference Section for another way to translate error codes.